And sleep quality seems to improve whether the weight loss is achieved through dieting alone or by combining diet with exercise, researchers from Johns Hopkins found.

"We found that improvement in sleep quality was significantly associated with overall weight loss, especially belly fat," the study's senior author, Kerry Stewart, a professor of medicine at the Johns Hopkins University School of Medicine and director of clinical and research exercise physiology, said in a Hopkins news release.

The study involved 77 overweight or obese people with
type 2 diabetes or pre-diabetes. The participants were divided into two groups: those who dieted to achieve weight loss, and those who dieted and also exercised.

The participants also completed a sleep survey at the beginning and end of the study. In the survey, they provided information on sleeping difficulties, such as sleep apnea, daytime sleepiness, insomnia, as well as excessive or restless sleep. The researchers also measured the participants' belly fat and body mass index (a measurement based on height and weight) at the beginning and end of the study.

Over the course of six months, 55 people completed the study. Both groups lost an average of about 15 pounds and also shed about 15 percent of their belly fat, the investigators found.

The study also revealed that all of the participants were sleeping better by the end of the study, with both groups improving their sleep quality equally by 20 percent.

"The key ingredient for improved sleep quality from our study was a reduction in overall body fat, and, in particular belly fat, which was true no matter the age or gender of the participants or whether the weight loss came from diet alone or diet plus exercise," Stewart explained in the news release.

The study authors pointed out that proper sleep quality is important for both physical and mental health. Disruptions in sleep can increase risks for high blood pressure, heart attack, stroke and irregular heartbeat. And the risk for sleep problems is greater for people who are obese, the authors noted.

The study is expected to be presented on Tuesday at the American Heart Association meeting in Los Angeles. The data and conclusions of research presented at medical meetings should be considered preliminary until published in a peer-reviewed journal.